1. Field of the Invention
Our invention is a horizontal roof strain indicator which employs tensioned wire between two separated roof bolts.
2. Description of the Prior Art
The basic invention over which our invention is an improvement is the horizontal roof strain indicator (HORSI). A full description of the HORSI can be found in the U.S. Bureau of Mines Information Circular/1974, IC 8630 on pages 92-96, and in the "Technology News" from the Bureau of Mines. Essentially this prior art discloses two spaced caps that form an assembly pair with a tensioned wire connected between them. One of the caps anchors the wire while the other measures the linear displacement on the wire with a removable dial indicator. Each cap is fixedly mounted on the lower end of an in situ mine roof bolt spaced from about 4 to 8 feet apart. Within the measuring cap a spring tensional plunger is linearly aligned with the wire at one end and, when it is attached, the dial indicator. As one or both of the firmly anchored rock bolts move vertically due to displacements of the mine roof, the reading on the horizontal stretched wire changes from its initial setting. These changes--which can indicate displacements as small as 0.001 of an inch-- can be related to horizontal strain on the wire and an unstable mine roof condition transmitted from the roof bolts.
Our invention employs the same basic HORSI arrangement but, with rotatable caps that can be fixed at different angles. This rotational capability of the wire mounting caps assures that a straight pull will always be transmitted to the wire spring plunger regardless of the location of the roof bolts to which attached. It also allows installation of the HORSI without the necessity of the two faces of the caps being parallel when installed. In addition, the wire may be removed from one assembly end and reused with a different spaced similar assembly or it may be used in series with a plurality of assembly pairs. Thus, the prior art trial and error method of aligning the wire with the proper wire tension is eliminated and replaced with a quicker and more versatile invention.
The primary object of our invention is an improved horizontal roof strain indicator.